Matakuliah : M0564 /Pengantar Sistem Basis Data
Tahun : 2008

Pada akhir pertemuan ini, diharapkan mahasiswa akan mampu :
• Mahasiswa dapat menerangkan konsep dan terminologi pemodelan relasional. (C2)
3
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• Terminology
• Integrity Constraints
• Views
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• A relation is a table with columns and rows.
– Only applies to logical structure of the database, not the physical structure.
• Attribute is a named column of a relation.
• Domain is the set of allowable values for one or more attributes.
• Tuple is a row of a relation.
• Degree is the number of attributes in a relation.
• Cardinality is the number of tuples in a relation.
• Relational Database is a collection of normalized relations with distinct relation names.
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Mathematical Definition of Relation
• Consider two sets, D
1
5}.
& D
2
, where D
1
= {2, 4} and D
2
= {1, 3,
• Cartesian product, D
1 of D
2
.
 D
2
, is set of all ordered pairs, where first element is member of D
1 and second element is member
D
1
 D
2
= {(2, 1), (2, 3), (2, 5), (4, 1), (4, 3), (4, 5)}
• Alternative way is to find all combinations of elements with first from D
1 and second from D
2
.
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Mathematical Definition of Relation
• Any subset of Cartesian product is a relation; e.g.
R = {(2, 1), (4, 1)}
• May specify which pairs are in relation using some condition for selection; e.g.
– second element is 1:
R = {( x , y ) | x  D
1
, y  D
2
, and y = 1}
– first element is always twice the second:
S = {( x , y ) | x  D
1
, y  D
2
, and x = 2 y }
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Mathematical Definition of Relation
• Consider three sets D
1
D
1
 D
2
 D
3
; e.g.
, D
2
, D
3 with Cartesian Product
D
1
= {1, 3} D
2
= {2, 4} D
3
= {5, 6}
D
1
 D
2
 D
3
= {(1,2,5), (1,2,6), (1,4,5), (1,4,6), (3,2,5), (3,2,6),
(3,4,5), (3,4,6)}
• Any subset of these ordered triples is a relation.
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Mathematical Definition of Relation
• The Cartesian product of n sets ( D
1
, D
2
, . . ., D n
) is:
D
1
 D
2
 . . .
 D n
= {( d
1
, d
2
, . . . , d n
) | d
1
 D
1
, d
2
 D
2
, . . . , d n
 D n
} usually written as: n
X D i i = 1
• Any set of n -tuples from this Cartesian product is a relation on the n sets.
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• Relation schema
– Named relation defined by a set of attribute and domain name pairs.
• Relational database schema
– Set of relation schemas, each with a distinct name.

• Relation name is distinct from all other relation names in relational schema.
• Each cell of relation contains exactly one atomic
(single) value.
• Each attribute has a distinct name.
• Values of an attribute are all from the same domain.
• Each tuple is distinct; there are no duplicate tuples.
• Order of attributes has no significance.
• Order of tuples has no significance, theoretically.
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• Superkey
– An attribute, or a set of attributes, that uniquely identifies a tuple within a relation.
• Candidate Key
– Superkey (K) such that no proper subset is a superkey within the relation.
– In each tuple of R, values of K uniquely identify that tuple
(uniqueness).
– No proper subset of K has the uniqueness property (irreducibility).
• Primary Key
– Candidate key selected to identify tuples uniquely within relation.
• Alternate Keys
– Candidate keys that are not selected to be primary key.
• Foreign Key
– Attribute, or set of attributes, within one relation that matches candidate key of some (possibly same) relation.
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• Null
– Represents value for an attribute that is currently unknown or not applicable for tuple.
– Deals with incomplete or exceptional data.
–
Represents the absence of a value and is not the same as zero or spaces, which are values.
• Entity Integrity
– In a base relation, no attribute of a primary key can be null.
• Referential Integrity
– If foreign key exists in a relation, either foreign key value must match a candidate key value of some tuple in its home relation or foreign key value must be wholly null.
• Enterprise Constraints
– Additional rules specified by users or database administrators.
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• Base Relation
– Named relation corresponding to an entity in conceptual schema, whose tuples are physically stored in database.
• View
– Dynamic result of one or more relational operations operating on base relations to produce another relation.
• A virtual relation that does not necessarily actually exist in the database but is produced upon request, at time of request.
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• Contents of a view are defined as a query on one or more base relations.
• Views are dynamic, meaning that changes made to base relations that affect view attributes are immediately reflected in the view.
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• Provides powerful and flexible security mechanism by hiding parts of database from certain users.
• Permits users to access data in a customized way, so that same data can be seen by different users in different ways, at same time.
• Can simplify complex operations on base relations.
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• All updates to a base relation should be immediately reflected in all views that reference that base relation.
• If view is updated, underlying base relation should reflect change.
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• There are restrictions on types of modifications that can be made through views:
Updates are allowed if query involves a single base relation and contains a candidate key of base relation.
- Updates are not allowed involving multiple base relations.
- Updates are not allowed involving aggregation or grouping operations.
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• Classes of views are defined as:
– theoretically not updateable;
– theoretically updateable;
– partially updateable.
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